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. 2019 Apr 16;10:407. doi: 10.3389/fpls.2019.00407

Figure 2.

Figure 2

Putative S-locus structure of Pyrus, Prunus, and Solanaceae species. In all cases, the S-locus contains an S-RNase gene (purple arrow), which acts as the pistil S-determinant. For Pyrus and Solanaceae species, this S-RNase gene is surrounded by a large number of SFBB/SLF genes (blue arrows) which are proposed to make up the pollen S-determinant. For Pyrus, the expected number of F-box genes (SFBB genes) is approximately 18–20, which is comparable to the observed number of F-box genes (SLF genes) in Petunia (Solanaceae). It is expected that the size, orientation, and position of these F-box genes relative to the S-RNase gene are variable between S-haplotypes. In Prunus, the pollen S-determinant is the SFB gene (green arrow) that is located closest to the S-RNase. The three surrounding SLFL genes (dark blue arrows) are relatively closely related to the SFBB and SLF genes of Pyrus and Solanaceae, respectively. It is suggested that they function as the general inhibitor in the Prunus SI system. Figure based on DeFranceschi et al. (2012).